In Live preferences, set the Ableton Push (Port 2) Input to Track On and
Remote On. Set the Ableton Push (Port 2) Output to Track On and Remote
On.

Create two MIDI tracks. Add the Push.LinearSeq device and a virtual
instrument device to the first track. Set the 'MIDI Outut To Push' to
PathMIDI1 in the Push.LinearSeq device. Set the first track to 'Monitor
In' mode. Set the MIDI From device to 'Ableton Push (Port 2)'.

Add the PathMIDI.Receive
to the second track. Set the MIDI from to 'PathMIDI1' in the
PathMIDI.Receive device. Set the MIDI to device to 'Ableton push (User
Port)'.

Press and hold the tap tempo button to set the phrase length for each pitch independently.